--do the students exercise a week? -Once or twice.A. How longB. How often C. How ma

问题补充：

----do the students exercise a week? ---- Once or twice.

A. How longB. How often C. How many times

答案：

解析：句意:-这些学生一周锻炼几次？-一次或两次。how long 多长时间，对一段时间提问；how often 多久一次，提问频率；how many times 多少次，time 表示三次或以上。故选B。